Method and apparatus for concentrating liquid-solids mixtures



Dec. 30, 1969 P. E. TODD METHOD AND APPARATUS FOR CONCENTRATINGLIQUID-SOLIDS MIXTURES 4 Sheets-Sheet 1 Filed July 51, 1967 Light 53Vacuum 53 Light 2 Discharge v INVENTOR PH/L /P E. TODD BY mug,

ATTORNEYS Dec. 30, 1969 P. E. Tom: 3,486,543

METHOD AND APPARATUS FOR CONCENTRATING LIQUID-SOLIDS MIXTURES Filed July5 4 Shets-Sheet 2 PHIL/P 5. r000 BY JM, W/Vut,

ATTORNEYS Dec. 30, 1969 P, E. TODD 3,486,548

METHOD AND APPARATUS FOR CONCENTRATING LIQUID-SOLIDS MIXTURES Filed July51. 1967 4 Sheets-Sheet 4.

CHOPPED FRUIT' v SYRUP IMIXING- z-coouwe PASTURIZING-3 INVENTOR.CANNlNG-4 PHIL/P E. 7000 BY #04, Mew 44x, m W

ATTORNEYS United States Patent O Int. Cl. B01d 1/22 U.S. Cl. 159-5 9Claims ABSTRACT OF THE DISCLOSURE Concentrating method in which hydrousmaterial containing liquid and solids (e.g., sugar syrup with pieces offruit) is fed continuously to one end of a horizontal heated surface andmoved continuously across the surface in the form of a thin layersection of regulated depth, with discharge of the concentrate at theother end thereof. During transit the material is subjected to a partialvacuum. Also apparatus for carrying out the foregoing method in whichconveying means moves across a horizontal heated surface and serves todivide the material on the surface into successive layers. The materialto be concentrated is fed to one end of the surface and removed as aconcentrate from the other end. A cover or hood covers the surface andis evacuated for removal of vapors.

This invention relates generally to methods for the concentration ofmixtures of liquids and solids, such as jams, preserves and marmalades,and to apparatus for carrying out such methods.

In the food processing industry it is frequently necessary toconcentrate mixtures containing liquid and solids, to a relatively highconsistency or viscosity. Particular reference can be made to themanufacture of so-called jams, preserves, and marmalades which containsugar syrup and solids and are commonly classed as high solidshigh acidfoods. The processing of such foods involves concentration byevaporation to a solids content which may be of the order of from 6070%.The conventional concentrating methods and equipment commonly employedfor such mixtures are unsatisfactory for a number of reasons.Particularly, they tend to cause impairment of flavor due to overcookingand excessive localized heating. Also conventional equipment is notwell-adapted to high capacity continuous plant operations. Thedifliculties experienced with conventional methods and equipment areaccentuated when the material contains coarse pieces of fruit or likematerial, and it is desired to retain comparable pieces in the finalproduct. Conventional methods and equipment tend to crush or pulp suchsolids and they may be subjected to heat injury and flavor impairment bylocalized overheating and loss of essences through prolonged evaporationperiods.

In general it is an object of the present invention to provide animproved concentrating method and apparatus capable of effectivelyconcentrating mixtures of the type referred to above and characterizedby continuous operation.

Another object of the invention is to provide an improved concentratingmethod and apparatus capable of producing concentrated foods mixtureswith superior flavor.

Another object of the invention is to provide an improved concentratingmethod and apparatus capable of handling and concentrating mixtures ofthe type having fruit or like solids in the form of relatively coarsepieces.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment is set forth indetail in conjunction with the accompanying drawing.

Summary of the invention A method for the concentration of hydrousmixtures containing liquid and solids. The mixture is suppliedcontinuously to one end of a horizontal heated surface to form a layerof the material. Successive layer sections are moved continuously fromthe feed end of the horizontal surface to the other discharge end.During transit the layer sections are subjected to a partial vacuumwhereby progressive evaporation of moisture occurs. At the otherdischarge end of the heated surface the concentrated material iscontinuously discharged. The apparatus for carrying out the methodconsists of a metal wall or plate which is disposed horizontally andwhich forms the substantially horizontal surface. Means is provided forcontinuously supplying heat to this wall. A hood or enclosure isdisposed over the upper surface of the wall and is adapted to beevacuated. Means are provided for continuously supplying the mixture tobe concentrated to one end of the horizontal plate, whereby the mixturespreads as a layer over the upper surface of the plate. Also conveyermeans is provided for isolating successive sections of the mixture andfor moving the same over the upper surface of the plate, toward theother discharge end of the same. In addition means is provided forcontinuously removing the concentrated material from the other dischargeend of the wall.

Referring to the drawing:

FIGURE 1 is a side elevational view illustrating concentrating apparatusincorporating the present invention;

FIGURE 2 is an end view of the apparatus shown in FIGURE 1, lookingtoward the right hand end of FIG- URE 1;

FIGURE 3 is an end view looking toward the left hand end of FIGURE 1,and partly in section;

FIGURE 4 is an enlarged section showing the feed end of the apparatus;

FIGURE 5 is a detail in section illustrating the discharge end of theapparatus;

FIGURE 6 is a side view in section showing the heating jacket andassociated parts;

FIGURE 7 is a plan view of FIGURE 6;

FIGURE 8 illustrates equipment that may be employed with the apparatusof FIGURES I7; and

FIGURE 9 is a schematic view illustrating my method employed for themanufacture of fruit preserves.

DESCRIPTION OF PREFERRED EMBODIMENTS My method can best be described andunderstood after a description of the apparatus shown in FIGURES 16inclusive. It consists of a supporting frame 10 carried by the standards11. The frame 10 may include the side structural channels 12 secured tosuitable laterally extending members (not shown). This frame serves tosupport an assembly 13 (FIGURES 5 and 6) which includes a flathorizontal heat transfer plate 14 made of suitable material such asstainless steel. The underside of the plate 14 is provided with asteamheated jacket 16. At one end of the apparatus the jacket connectswith a steam inlet pipe 19, and at the other end there is a connectionwith the condensate pipe 20. Spacers 22 are shown inserted between theplate 14 and the wall 17 of the steam jacket. They serve to stiffen theplate 14 and to provide a zigzag passage for flow of steam.

Overlying the horizontal plate 14 (FIGURE 1) there is a conveyer 32 ofthe endless chain type. At the feed end of the apparatus the conveyerconsists of the shaft 33 which is carried by bearings 34 and which isprovided with the chain sprockets 36. At the discharge end of theapparatus there is a similar shaft 37 carried by bearings (not shown)and provided with sprockets 39. The endless chains 44 engage thesprockets 36 and 39, and serve to carry the spaced flights 45. Theseflights are in the form of slats which extend substantially the fullwidth of the wall 14, and are adapted to ride upon and wipe over theupper surface of the plate 14. They can be made of suitable materialsuch as Teflon, Kel-F, or nylon. Preferably they have suflicientflexibility to ensure good wiping contact over their entire length withthe upper surface of plate 14.

The upper run of the endless chains 44 are shown supported by aplurality of idler sprockets 46 which in turn are carried by the idlershafts 47. These shafts are suitably journalled at their ends bybearings (not shown). The conveyer chains are driven by suitable means,such as an exterior drive sprocket 48 which is shown mounted upon oneend of the shaft 33. Preferably the drive is variable whereby the speedof operation of flights 45 can be adjusted for optimum operation undergiven operating conditions.

A sealed hood or cover 49 encloses the space over the heat transferplate 14. The side walls of the hood are shown with margins 50 that areadjacent the inner faces of the channels 12, and secured to the sideedges of the heat transfer plate 14. This hood is shown provided withducts 51 which can be connected by conduits (not shown) to a suitableevacuating system. The evacuating system may for example consist of avapor condenser and a vacuum pump. Also the hood can be provided withglass covered inspection openings 52 and light fittings 53. One end wallof the hood is provided with a quick opening closure 54 and the otherend wall 55 has a gasket sealed clamping 55a to the corresponding endmargin of plate 14.

As shown particularly in FIGURE 4, at the feed end of the apparatusthere is a feed duct 56 which is divergent or fan-shaped as shown inFIGURE 2. The lower apex end of this duct is connected with the feedsupply pipe 57 and may also be provided with a normally closed drain 58.The plate 14 is provided with a slot 59 extending over substantially itsentire width and which is in free communication with the upper open endof the duct 56. The feed material pumped through pipe 57 spreads orflows laterally over the adjacent upper surface of the plate 14 in thevicinity of the slot 59, and successive layer sections or portions areisolated between the travelling flights 45 and caused to be movedcontinuously over the upper surface of plate 14. The depth of the layerportions between each set of adjacent flights 45 is regulated orcontrolled by the rate of feed through the pipe 57 and the speed ofmovement of the flights 45. For a given feed mix and set of operatingconditions the depth of the layer remains substantially constant at thefeed end of plate 14. In general this layer can be relatively thin andof such depth as to insure substantially complete coverage of plate 14between the flights, for the entire length of the. apparatus. This depthmay vary somewhat in different runs depending on such factors as theconsistency or viscosity of the feed mix and the amount of moisture tobe removed.

At the discharge end of the apparatus (FIGURE there is a somewhatsimilar arrangement for removing concentrate. Thus a fan-shaped duct 60has its upper end communicating with the space above the plate 14through the transverse slot 61. The apex end of duct 60 connects withthe discharge pipe 62, which may be connected with means such as a pumpor a barometric leg, to maintain a vacuum seal. The material being movedalong by the flights 45 is delivered to the region of the slot 61,whereby it flows down by gravity through the duct 60 and pipe 62.

FIGURE 8 schematically illustrates equipment which can be used with theapparatus shown in FIGURES l-4. The concentrating apparatus is indicatedat 66 and is shown with its hood connected by conduit 67 with the vaporcondenser 68. This condenser may be of the water jet type and is shownconnected to the evacuating pump 69. A mixing tank 70 is shown forreceiving the ingredients of the mix, and is connected by pump 71 withthe heat exchanger or cooler 72. Water connections 73 and 74 are shownfor circulating cold water through the cooler. From the heat exchanger72 the mixture is introduced into the concentrator 66 by way of pipe 57at a controlled temperature level which is above the vaporization pointat the partial vacuum maintained within the concentrator. For example,where the partial vacuum maintained is of the order of 28 inches mercurycolumn, the temperature of the mix in a typical instance may be of theorder of to F. Concentrate is continuously removed from the dischargeend of the apparatus 66 through pipe 62. Pump 63 serves to pass thisconcentrate through the heater 64 which serves to elevate thetemperature to a suitable level for pasteurization, such as 200 F. Theconcentrate can then be delivered to a holding tank where it is held fora sufficient period to ensure pasteurization, after which it isintroduced into containers for marketing.

It is desirable to provide the system of FIGURE 8 with automaticcontrols such as schematically indicated. Thus a valve 76 is shown forcontrolling the steam supplied to the jacket 70a of the mixer 70. Thisvalve is connected for automatic control to the temperature controller77, whereby when the temperature level of the mix reaches a desiredlevel (e.g., 200 F.), the steam supply is automatically reduced toprovide only sufficient heat to maintain the temperature at that level.The cold water supply to heat exchanger 72 is shown controlled by valve78, which in turn is connected to temperature controller 79 and recorder80, whereby the water supply is regulated to maintain the temperature ofthe mix leaving the heat exchanger at a desired constant value. Thesteam supply to the concentrator heating jacket 16 is shown controlledby valve 81, which in turn has a control connection to the pressureresponsive device 82, whereby a constant steam pressure is maintained inthe jacket.

A suitable density responsive device 83 (e.g., a device of the gamma raytype) is inserted in the discharge line 62 to the pump 63. Densityvariations are translated into control values (e.g., electricalvoltages, pneumatic pressure, etc.) by associated device 84, wherebycorrelated control signals are derived and applied by the indicatedcontrol connections 86 and 87 to the variable driving motor 88 of theconcentrator, and the variable motor drive 89 of the feed pump 71. Thearrangement is such that as the density increases above a desired value,the drive speed of pump 71 is increased to increase the rate of supplyof the mix, and simultaneously the rake conveyor 32 of the concentratoris driven at an increased speed to provide a reduced holding time on theplate 14.

The interior of the concentrator hood 49 is shown connected to a vacuumresponsive device 72'. This device connects with the device 73 whichderives control signals applied by connections 74' and 75 to vent valve76 and variable pump drive 89. This arrangement is such that pump drive89 is inoperative unless a predetermined vacuum exists in the hood ofthe concentrator. Also if the vacuum should become excessive, vent 76 isopened to break the vacuum.

The steam input to the heater 64 is shown provided with a control valve91 that is controlled by the temperature responsive device 92. Thus theoutput from this heater is maintained at a desired constant temperaturelevel (e.g., 200 F.).

The controls described above operate as follows. After introducing thedesired mix into the mixer 70, steam is supplied at a rate suflicient toelevate the mix temperature to a desired level, after which the steamsupply is automatically reduced to a value sufiicient to maintain thedesired temperature. The pump 71 cannot operate until a desired minimumvacuum has been provided in the concentrator by vacuum pump 69. As themix is being pumped through the cooler the cold water supply iscontrolled to provide a constant temperature level (e.g., 108 F.) forthe output being supplied to the concentrator. The conveyer of theconcentrator and also the rate of feed of the mix are controlled by thedensity of the output of the concentrate, whereby the density ismaintained at a desired constant value. The heater 64 is controlledwhereby its output is maintained at a desired level.

FIGURE 9 schematically illustrates the concentrating apparatus describedabove, together with steps in flow sheet form for the manufacture of afruit preserve or like product. By fruit I have reference to the variousfruits and berries such as are used in the manufacture of jams,preserves and marmalades, including citrus, pineapple, peaches,cherries, apricots, figs, plums and the various berries, includingstrawberries, blackberries, cranberries, blueberries and the like. Thesource fruit may be fresh or may have been frozen or thawed. It isprepared by various conventional methods, such as cleaning and removingof peels, seeds and the like. The fruit may be whole (e.g.,strawberries) or may be chopped or sliced to a desired size and shape.In some instances the pieces may be coarse cube-like chunks, and inother instances they may be slices or strips of substantial length. Step1 represents the mixing in mixer 70 of such chopped fruit with asuitable sugar syrup, or with the requisite amounts of sugar and waterto make the syrup. Generally it is desirable to carry out this mixingstep at an elevated temperature such as from 160 to 212 F. Thereafterthis mixture, which may have a solids content of from 50 to 60%, iscooled by exchanger 64 in step 2 to a predetermined lower temperaturelevel, such as for example a temperature of the order of 105 to 115 F.This mixture is then pumped at a continuous rate through pipe 57 of theconcentrating apparatus 66. As the mixture passes upwardly through thedivergent duct 56, and through the slot 59, it spreads or flowslaterally to form a relatively thin layer extending over the adjacentarea of the plate 14, and successive layer portions or sections areisolated between adjacent slats or flights 45. These isolated layerportions or sections are moved continuously toward the left as viewed inFIGURE 6, and during such movement heat is supplied through the plate 14from the jacket 16, and the mixture is subjected to a partial vacuum.The partial vacuum is such as to cause effective evaporation of moisturewithout causing violent boiling. In practice partial vacuumscorresponding to from 26 to 28 inches mercury column have been used. Theheat supplied by steam in the jacket 16 can be such as to transfer heatthrough the plate 14 at a rate sufficient to maintain the temperature ofthe mixture at or about a suitable level for effective heat transfer.Each isolated portion or section of the mixture becomes graduallyconcentrated by evaporation as it moves over the plate 14 until thefinal concentration desired is attained as the material is delivered tothe space adjacent the slot 58. The concentrate then flows through theconduit 57, after which it is subjected to pasteurizing 3, andintroduced into containers in step 4. The holding time within theconcentrator is controlled by the speed of the conveyer and may varysomewhat depending upon the character of the feed mix and the amount ofwater vapor removed. In practice, holding times ranging from to 25seconds have been used with good results.

As an isolated layer portion or section is being moved along the uppersurface of plate 14, some agitation takes place within the layer ofmaterial, due to the tendency of material immediately in contact withthe plate 14 to remain stationary. Thus circulation takes place withinthe layer which is conducive to good heat transfer and effectiveevaporation of moisture.

The speed of movement of the conveyer flights 45 should be such that forthe mixture being processed, the material does not tend to pile up as athick mass immediately in advance of the flights. It has been found thatwith conveyer flight speeds of the order of from 1.5 to 2.5 feet persecond, and with the apparatus being used on materials such as jams,preserves and marmalades, no serious pile up tends to occur in advanceof the flights, but on the contrary the fluidity of the materialundergoing evaporation is sufficient to maintain a layer extendingcompletely between adjacent flights and over the entire width of plate14.

It has been found that my method and apparatus can be used successfullyin the concentration of mixtures containing solids of considerable size,as for example, whole berries, cubes or chunks which may be of the orderof from A to A" in diameter, or slices which may be of the order of fromV to /s" thick, to /2" wide, and /2 to 1 /2" in length. The presence ofsuch solids does not interfere with effective concentration of theover-all mass of material. Heat is transferred to such solids not onlyby direct contact with the plate 14, but also by contact withsurrounding heated liquid. The d1- mensions of the solids may be suchthat portions extend above the adjacent liquid level in the layersections moving over the plate 14. It has been found that when suchcoarse pieces are present, they are not pulped or seriously reduced insize during transit through the concentrating apparatus.

In general it has been found that jams, preserves and marmaladesconcentrated by use of my method and apparatus have superior flavorcharacteristics. The flavor more nearly approximates the flavor of thefruit from which the mixture is made. This advantage is attributed tothe conditions existing in the concentrating apparatus which are such asto avoid injury to heat-sensitive flavor constituents. Extendedretention of material within the concentrator, with resultingover-heating, is avoided. Also localized over-heating is avoided due tothe fact that the mixture is always under motion while it is in contactwith the heated plate 14. The rapid rate of product throughput and thehigh evaporation rates result in retention of essences that wouldotherwise be lost in conventional methods and apparatus, and also servesto prevent or minimize detrimental product breakdown.

An example of my invention is as follows: The heated plate 14 had aneffective length of about 8 ft. and an effective heat transfer area of16 sq. ft. The drive to the conveyer was such that the conveyer flights45 moved at a speed sufricient to provide a holding time of 20 seconds.The flights were located about 12 inches apart on the chains 44. Themixture prepared in step 1 comprised fresh strawberries averaging about1 inch in diameter, together with sugar and water. The proportions werelbs. of whole strawberries to lbs. of canning sugar and 10 lbs. ofwater. This mixture was heated to a temperature of about 147 F. for aperiod of about 5 minutes, after which it was held for about 5 minutesand then pumped continuously through the cooler 68 to cool the mixtureto about 106 F. This mixture was fed continuously to the concentratingapparatus at a rate of about 100 lbs. per minute (60 Brix). A partialvacuum was maintained corresponding to 26.5 inches mercury column. Theconcentrate was delivered from the concentrator at the rate of 80 lbs.per minute (68 Brix) and contained about 70.3% solids. It was pumpedcontinuously through the heater 59 to elevate its temperature to 200 F.and then held in a tank for a period of about 5 minutes forpasteurization. Preserves made in this fashion were characterized byexcellent flavor and keeping characteristics. The whole strawberrieswere clearly visible in the final product.

While I have described my method and apparatus as being particularlyadapted for the manufacture of jams, preserves and marmalades it shouldbe understood that it can be applied to a wide variety of mixturesincluding those that are somewhat difficult to concentrate byconventional apparatus. Particular reference can be made to theconcentration of vegetable and fruit purees, fruit juices, meat slurriesand the like.

In some instances it may be desirable to effect pasteurization beforeconcentrating, in which event pasteuriziug temperatures and holdingtimes are applied in conjunction with mixing.

I claim:

1. A method for the concentration of hydrous mixtures containing liquidsand solids comprising continuously supplying a quantity of the mixtureto be concentrated to the feed end of a substantially horizontal heatedsurface, introducing said mixture as a continuous layer from below andthrough said surface onto one feed end thereof, as said mixture isintroduced onto said surface, sequentially isolating successive portionsor sections of said mixture layer and continuously moving successivelayer sections one after the other over said surface from the feed endto the opposite discharge end of said surface, maintaining a partialvacuum above said surface during movement of said layer sectionsthereover, the layer sections being progressively concentrated byevaporation during movement over said surface, and continuously removingthe concentrated mixture sections down through said discharge end ofsaid surface.

2. A method as in claim 1 in which the hydrous mixture consists of sugarsyrup together with fruit solids in the form of coarse pieces.

3. A method as in claim 1 in which the speed of movement over saidsurface and the rate with which the mixture is supplied are varied inresponse to variations in the density of the concentrated mixturesections removed from said discharge end of said surface.

4. A method as in claim 1 in which the hydrous mixture is introducedonto said feed end of said surface as a layer of generally uniformthickness which extends across substantially the full width of saidsurface so that subsequent spreading of said mixture over said surfaceis obviated.

5'. A method as in claim 1 in which said layer sections are agitatedduring movement thereof over said surface.

6. Apparatus for the concentration of hydrous mixtures comprising afixed metal heat transfer plate forming a substantially horizontalsurface, means for heating the underside of said plate, an enclosuredisposed over and surrounding the surface and defining an evacuatedspace thereabove, means for continuously supplying a hydrous mixture tobe concentrated as a generally uniform layer up through and upon one endof the horizontal surface whereby the mixture may be caused to flow overthe surface, means for isolating said mixture into successive portionsor sections and for continuously moving such successive layer portionsor sections over said surface and toward the other discharge end of thesame, and means for continuously removing concentrated mixture layerportions or sections down through the other discharge end of thesurface.

7. Apparatus as in claim 6 in which the means for isolating andcontinuously moving successive layer portions or sections over saidsurface consists of a conveyer overlying said surface, said conveyerhaving spaced flights mounted thereon and extending laterally acrosssaid surface and in contact therewith, said flights being movedcontinuously from one end of the plate to the other discharge endthereof.

8. Apparatus as in claim 7 in which the means for supplying the materialto be concentrated to one end of the horizontal surface consists of anupwardly extending duct having its upper open end communicating with aslot extending across said surface, and in which the means forcontinuously removing concentrated material consists of a downwardlyextending duct having its upper open end communicating with another slotlikewise extending across said surface adjacent the other end thereof.

9. Apparatus for the concentration of hydrous mixtures comprising ametal heat transfer plate forming a fixed substantially horizontalsurface means for heating said plate, an enclosure disposed over saidsurface and enclosing said plate and defining a space above said surfacewhich is, means for continuously supplying a hydrous mixture to beconcentrated to one end of said surface whereby said mixture ispositioned to be flowed over said surface in the form of a layer, meansmovable within said space for isolating and continuously movingsuccessive layer portions or sections over said surface from said one tothe other discharge end of the same, and means for continuously removinga concentrated mixture from said other discharge end of said surface;said means for moving said mixture over said surface consisting of aconveyor overlying said surface, said conveyer having spaced flightsmounted thereon and extending transversely thereof and laterally acrosssaid surface in contact therewith, said flights being moved continuouslyfrom said one end of said surface to said discharge end thereof to movesaid layer sections along said surface toward said discharge end; saidmeans for supplying said mixture to said one end of said surfaceconsisting of an upwardly extending duct having its upper open endcommunicating with a slot extending across said surface; said means forcontinuously removing said concentrated mixture from said discharge endof said surface consisting of a downwardly extending duct having itsupper open end communicating with another slot likewise extending acrosssaid surface adjacent said discharge end thereof.

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